Particle track for a slowly drifting 80-micron-diameter neutrally-buoyant particle, as captured by the DDPIV camera I built for my thesis. Each grid square corresponds to 10 microns in real space. As seen from the jitter in Z (the depth direction), the position of the particle is resolved to within 50 microns of the mean path—in other words, its position is resolved nearly within its size. In X and Y the system performs around 2 or 3 times better.